Physiology Flashcards
Ventilation is
The exchange of air between the atmosphere and the alveoli. The volume of air moving out of or into the lungs at a given time
minute ventillation
Tidal volume times breaths per minute
alveolar ventillation
minute ventillation corrected for physiologic dead space
What happens to the FEV1 over FVC ratio in obstructive pulmonary disease
it goes down because the FEV1 decreases more than the FVC does, “volume of air that can be forcefully expired decreases, especially during the first second.”
What happens to the FEV1/FVC in restrictive lung disease
Goes up because FVC decreases more than FEV1
What is the rough calculation of anatomic dead space
Your wt in pounds
What is functional or alveolar dead space?
The volume of air that ventilates alveoli that do not participate in the perfusion process. This is most commonly due to a ventilation perfusion defect (V/Q mismatch). Can be unavailable for gas exchange due to lack of blood supply (embolus) or some sort of ventillation issue to that alveoli.
To increase alveolar ventillation, which is a more useful method of minimizing alveolar dead space
Slow deep breathing over fast shallow breathing.
Normal tidal volume
about 500ml
Normal anatomical dead space
about 150
Pressure =
force per unit area
If I say the pleural pressure is -4, that really means what
It is 756mmHg, 4 less than atmospheric/barometric
Pressure difference between alveolus and mouth(atmosphere) determines flow into and out of lungs
True
What determines the inflation of the lung
Transpulmonary pressure: the difference between the pressure in the alveolus and the pressure in the IP space
How do we measure IP pressure
Esophageal pressure (insert a balloon catheter into the esophagus)
Compliance relates the change in volume of a closed space to the change in pressure distending it
true
Decreased compliance found in what type of lung disease
restrictive lung disease…diseases that stiffen the lungs like fibrosis or pulmonary edema
What does a compliance curve look like
Lung volume on the y axis, transpulmonary pressure on the x axis. Hysteresis exists in the compliance curve. This is because during inspiration, the lung begins at low volume where liquid molecules are closest together. The intramolecular force between these lipid molecules is much higher than the intramolecular force between liquid and air. Thus, the compliance of the lung is lower during inspiration than it is during expiration.
Surfactant
reduces surface tension and prevents SMALL airspace (alveoli) from collapsing. it is mostly phospholipid and this alowsit to separate the bonds between liquid molecules
What two major factors determine lung compliance?
Tissue Properties: lung contains large amounts of collagen and elastin connective tissue fibers that account for about 1/3 of elastance. ALSO, the alveoli are interconnected which helps counteract collapse.
Surface Forces: Surfactant
WHat is the most important factor in determining airway resistance
Radius of the Tube
What is the significance of the radius of the airway being the greatest factor in determining airway resistance
People with increased airway resistance (asthmatics during attack) will breathe at a higher lung volkume because it opens up the airways more.
What are two othe rmajor factors that determine airway resistance in the bronchos/bronchioles
Contraction of bronchial smooth muscle, and density and viscosity of inhaled gas.
Define the respiratory quotient
Volume of CO2 produced/ volume of O2 consumed
Movement of O2 and CO2 is a process of
diffusion: movement down a partial pressure gradient
Fick’s Law of Diffusion
Volume or flux= (area available to diffusion/ thickness of the barrier) x D x (p1-p2)
Describe the change in partial pressures of oxygen and CO2 as air moves from the dry outside air into the lungs and through the circulation
Dry outside air: PO2 = 160mmhg, PCO2= 0
Humidified tracheal air= PO2 = 150, PCO2=0
In the alveolus= PO2= 100, PCO2= 40
Pulmonary artery= PO2= 40, PCO2= 46
Pulmonary Vein= PO2= 100, PCO2 = 40
THe pulmonary artery and vein values switch in the capillaries after CO2 comes into the blood and O2 leaves.
What is the alveolar ventilation equation and what is its significance>
It is: PACO2 = k x CO2 production/alv ventillation
It is significant because it shows that if CO2 production is constant, and it usually is, then alveolar CO2 is determined almost purely by alveolar ventillation.
Knowing the relationship between alveolar CO2 and ventillation, what are the definitons of hyperventilation and hypoventilation
Hyperventilation: A decrease in PACO2 due to alveolar ventillation being excessive
Hypoventilation: Increase in Alveolar CO2 because ventillation can’t keep up with production
Hypoxemia
Low oxygen in the blood
Hypoxia
Oxygen not being delivered to or utilized by the tissues.
What percentage of the oxygen carried in blood is dissolved?
1.5%….oxygen solubility is extremely low
98.5% of the oxygen carried in blood is bound to
Hemeglobin
4 heme groups in a hemeglobin molecule, each contains one atom of Fe2+ (Fe3+ is methemeglobin and it does not bind to O2) meaning that 4 oxygen molecules are bound by each hemoglobin molecule.
fact
What is the range of PO2 that hemoglobin is saturated at
between 60 and 100mmhg….this is a fairly wide range meaning that pO2 can drop quite a bit before we become hypoxic
What determines the gradient for )2 between the alveolus and the capillary? Is it the amt of oxygen bound to hemeglobin or the amt of oxygen dissolved in the blood
Dissolved in the blood. Keeps the gradient high
Describe what the oxygen hemoglobin dissociation curve looks like
pO2 on the x axis. Hemoglobin saturation on the Y
What shifts the oxygen-hemoglobin dissociation curve to the right ( hemoglobin has less affinity for O2).
Increase in PCO2, decrease in pH, Inc in temperature, inc in 2,3 DPG…
THINK EXERCISE
What shifts teh oxygen heme dissociation curve left
The opposite
What is the percentage of CO2 that dissolves in the blood?
5-10%
What does most CO2 do in the blood
It undergoes transformation to bicarb in red blood cells. 70-80% is transported as Bicarb
Respiratory acidosis is and is caused by?
CO2 values that are above normal and thus drive the pH of the system down. May be caused by hypoventilation, airway obstruction, poor gas exchange, pneumonia or edema (screw up gas exchange).
Respiratory alkalosis
CO2 is too low. This is due to hyperventilation from being at high altitude, having a pulmonary embolism, having severe anemia). or it can be caused by stimulation of the medullary respiratory center (stroke, tumor, etc..)
Metabolic acidosis
Decreaseed HCO3-. This can be caused by increased production of fixed acids (lactic acid, ketoacidosis), ingestion of acids (aspirin, methanol, formaldehyde poisoning), decreased acid excretion due to renal failure, increased loss of HCO3 due to diarrhea.
Metabolic alkalosis
High HCo3 due to kidney excreting too much acid, vomitting, or excessive antacid intake.
Normal A-a gradient formula
age+4/4
What are the causes of hypoxemia
NORMAL A-a
- Hypoventilation
- decreased PiO2 (low partial pressure of inspired oxygen, low Oxygen in the air)
WIDENED A-a
- Diffusion limitation
- R to L Shunt
- V/Q mismatch
ABnormal diffusion almost NEVER causes hypoxemia at rest. May cause it at exercise. Why is this true
The normal transit time for and RBC through the pulm vasculature is .75s, it only takes about .25 secs for gas to diffuse. So Diffusion has to be extremely limited (reduced by three times or more) or transit time has to be incredibly faster than normal.100% O2 WILL CORRECT DIFFUSION LIMITATION.
R-L shunt
Hypoxemia DOES NOT CORRECT with 100% oxygen
V/Q greater than 1
dead space units
V/Q less than 1
shunt like units
V/Q mismatch is the most common cause of hypoxemia
TRUE
V/Q mismatch corrects with O2
True
Pulmonary vascular resistance high or low?
Low
Does pulmonary vascular autoregulate?
No. it just distends when intravascular pressure increases
Blood flow is lowest at the apex and highest at the base. Why?
Vascular resistance decreases from top to bottom, pressure drop increases. Pressure is higher in the base of the lungs which distends the vessels and drives the resistance down.
SO THE RULE IS BOTH BLOOD FLOW AND BLOOD PRESSURE INCREASE FROM APEX TO BASE
yes
What are the two conditions that may cause lung arteries and arterioles to constrict
hypoxia and hypercapnia/acidosis
Pulmonary blood flow is the cardiac output of the right heart, which is equal to the cardiac output of the left heart
True, also remember that pulmonary blood flow is directly proportional to the pressure gradient between the pulmonary artery and the left ventricle.
Hypoxiv vasoconstriction is only a good thing to acertain extent. If lung disease is not widespread, casoconstriction can serve a protective role by redirecting blood toward well ventilated areas without changing overall pulmonary vascular resistance. However, pulmonary vascular resistance goes up to high when lung disease is widespread
true
Five causes of hypoxemia
Low ventilation (FiO2) Hypoventillation
Diffusion problem
V/Q mismatch
Shunt
Increases in Crdiac output, increase distribution of O2 in what way
linearlly. There is a linear distribution between cardiac output and oxygen distribution
Hemoglobin content increases O2 linearlly
truth… hemeglobin content has a linear relationship with oxygen distribution
Partial pressure of O2 in the arteries does not have a linear effect on O2 because it relies on hb content
truth
